It has long been known that a "foam" of polyurethane can be prepared by reacting a polyisocyanate with a poly-hydroxy compound in the presence of a small amount of water which acts as a blowing agent. The water reacts with isocyanate groups producing carbon dioxide gas which forms small gas bubbles or cells in the "foam" when the polyurethane sets.
Such "foam" products have a structure made up of numerous individual cells which generally are constructed of a three dimensional skeletal structure of interconnected strands with membranes or windows joined to the skeletal structure such that they partition contiguous cells. The skeletal structure in these cellular materials is usually considerably thicker than the membranes or windows.
When the foam windows are removed, an open-celled reticulated foam is produced which permits fluids to flow through the remaining skeletal structure. A method for producing reticulated foam is described in U.S. Pat. No. 3,175,025 to Geen.
Porous ceramic bodies have been formed by coating polyurethane with a ceramic material of choice and then removing the polyurethane by dissolving, depolymerizing, hydrolyzing and so forth. See U.S. Pat. Nos. 3,833,386 and 3,845,181.
Ceramic filters have also been manufactured by coating a polyurethane foam of a selected configuration with a ceramic material and then burning the polyurethane out of the resulting ceramic body. See U.S. Pat. Nos. 3,090,094 and 4,396,565.
Methods of hydrolyzing polyurethane foam are described in U.S. Pat. Nos. 4,196,148 and 4,328,368.